The present invention relates to a gear transmission to be with an automatic transmission for vehicles and, more particularly, to a gear transmission suitable for an automatic transmission of the transverse type having its center axis arranged widthwise of the vehicle.
Since the vehicular automatic transmission is mounted together with the engine in the engine room, it is preferable to be as small and light as possible. In order to improve the power performance and fuel economy, it is also preferable that the number of gear stages to be set is as large as possible. It is, therefore, conceived to adopt a gear transmission which is enabled to set six forward gear stages by using three sets of planetary gear mechanisms, for example, as exemplified in Japanese Patent Laid-Open No. 56746/1991.
Here will be briefly described the gear transmission. As shown in FIG. 4, there are arranged on a common axis an input shaft 1 and an output shaft 2, between which are arranged on a common axis a first planetary gear mechanism 3 of the double-pinion type and second and third planetary gear mechanisms 4 and 5 of the single-pinion type, as recited from the side of the input shaft 1. The carrier 3C of the first planetary gear mechanism 3, the carrier 4C of the second planetary gear mechanism 4 and the ring gear 5R of the third planetary gear mechanism 5 are all connected to rotate together. Moreover, the sun gear 3S of the first planetary gear mechanism 3 and the sun gear 4S of the second planetary gear mechanism 4 are connected to rotate together. Still moreover, the ring gear 4R of the second planetary gear mechanism and the carrier 5C of the third planetary gear mechanism 5 are connected to rotate together, and the output shaft 2 is connected to that carrier 5C.
There are provided a plurality of clutches for connecting the input shaft 1 to a predetermined one of rotary elements. Specifically: a first clutch C.sub.1 is interposed between the input shaft 1 and the sun gear 3S of the first planetary gear mechanism 3; a second clutch C.sub.2 is interposed between the input shaft 1 and the carrier 4C of the second planetary gear mechanism 3; and a third clutch C.sub.3 is interposed between the input shaft 1 and the sun gear 5S of the third planetary gear mechanism 5. Moreover, a fourth clutch C.sub.4 and a first one-way clutch F.sub.1 are arrayed in series with each other and are arranged in parallel with the third clutch C.sub.3.
Here will be described brake means for fixing a predetermined one of the rotary elements. There are provided: a first brake B.sub.1 for fixing the sun gear 3S of the first planetary gear mechanism 3 and the sun gear 4S of the second planetary gear mechanism 4 integrated together; a second brake B.sub.1 for fixing the ring gear 3R of the first planetary gear mechanism 3; and a third brake B.sub.3 for fixing the carrier 3C of the first planetary gear mechanism 3, the carrier 4C of the second planetary gear mechanism 4 and the ring gear 5R of the third planetary gear mechanism 5 integrated altogether. Moreover, a second one-way clutch F.sub.2 is disposed in parallel with that third brake B.sub.3.
As a result, the gear transmission of the prior art thus constructed is enabled to set six forward and two reverse gear stages by applying/releasing the individual clutches and brakes suitably, thereby to improve the power performance and the fuel economy by the multiple stages.
The gear transmission of the prior art thus far described is constructed such that the input shaft 1 and the output shaft 2 are arranged on a common line while interposing the three sets of planetary gear mechanisms 3, 4 and 5 inbetween. Thus, the gear transmission is suited for an automatic transmission of the so-called "longitudinal type (for rear wheel drive)", in which the gear transmission is arranged longitudinally of the vehicle. In order to apply the gear transmission to the transverse type automatic transmission, however, a pair of counter gears 6a and 6b have to be arranged at the axial end portion, as illustrated by broken lines in FIG. 4, so that the power may be transmitted to a predetermined output member arranged in an axially central portion through a counter shaft 7 connected to those paired counter gears 6a and 6b. This arrangement increases the number of parts to be arranged in the axial direction and accordingly the axial length. As a result, the number of gear stages could be increased, but the entire construction is enlarged to cause a disadvantage that the mountability is deteriorated.